Wednesday, July 30, 2014

Two-eyed cyclops -- the plasticity of the brain

The brain is a remarkable thing.  Part of what's so remarkable about it is how it responds to and molds itself around experience.  Alfred Wallace exempted humans from the march of evolution because we are able to do so many things that can't be attributed to natural selection: calculus, the invention of televisions and robots, smell tar and Twinkies, none of which are abilities that we specifically can thank natural selection for since they are all recent.  We can do them because of our brain's adaptability, its ability to make sense of input it clearly isn't hardwired to understand.

Toy tin robot in the show. Boston MA United States. Picture taken by Jonathan McIntosh, 2003; Wikimedia
I remember lying in bed when I was a child, before I was even in kindergarten, closing one eye and then the other and noticing that I could clearly see the books on the bookshelf across the room with one eye but the same books were a blurry mass with the other.  This was just a fact of life, of idle interest to my 4-year old self but nothing more, and I don't think I ever thought to mention it to anyone. I was fine; I could read up close, I could see in the distance, just not with both eyes at once, so it didn't occur to me that anything was weird or wrong about that.  A routine eye exam at school found me out and I finally got glasses to correct this thing that wasn't really a problem.

As I've gotten older, my vision has gotten worse, each eye in its own way.  My eyes are equidistant from 20:20 in opposite directions, one myopic, the other hyperopic; I can still see without glasses, though not perfectly. And still, without my glasses, it's one eye working at a time.

Vision pathway; Weiss and Buchanan, The Mermaid's Tale, 2009
But think about what that means.  Without my glasses, light is pouring into both eyes, hitting my retina at essentially the focally right place in one eye, but all wrong in the other.  The curious thing, to me, is that my brain long ago learned not to pay attention to the blurry input, to only interpret the light waves hitting my retina in the 'right' place. How did it know which was right?

And at some point, in managing input anywhere along the continuum from my eyes to the furthest point I can see, my brain switches from paying attention to my right eye to paying attention to my left.  All the light waves are getting passed along in the same way to both eyes and on to my visual cortex -- I know this because if I close the 'good' eye, of course I'm seeing something, it's just blurry -- but at the very final step in the vision pathway, when my visual cortex is coordinating all the input into a single image, my brain dumps the blurry images and retains the clear.

But it's even more impressive, I think -- with my glasses on, my brain allows input from both eyes to make its way to the final image.  It's switching from monocular to binocular vision all the time.  Again, how does it know to do that?

My eyes as a metaphor for life
The plasticity of the brain isn't confined to the vision pathway, of course.  Plasticity defines the brain -- it's why we can meet new people, learn things, have new experiences, create memories, and then make sense of it all as we go.  Not only are we constantly making new synapses between neurons, we are still making new neurons well into old age, which is what makes our brains able to successfully make sense of all the information with which we're bombarded all the time.  Adaptability, or facultativeness, is so fundamental to evolutionary success that we think of it as a basic principle of life (see chapter 3, The Mermaid's Tale).

And yes, there's a larger point here.  The idea that some of us evolved 'for' sprinting, ping-pong, money-lending, economic prowess, or the ability to do well in 20th century school systems is based on, we think, a superficial understanding of evolution, and the way the brain works.  But it's an appealing one, one that too many scientists and journalists still believe.

Ideology assumes, science asks.


Robert Kopec said...

Re: "The brain is a remarkable thing"
Not just the brain, the human body of which the brain is only a part. I'm not sure there is any other animal with the kind of body capable of the full diversity of movements that humans are capable of, including the kind of detailed handiwork involved in making a basket or repairing a watch, a soccer players scoring a goal, or an actor mimicking a cat.

Anne Buchanan said...

Yes, absolutely. A violinist, an illusionist, a designer of pyramids.